The present invention relates to an infinitely variable cone-pulley, belt-type transmission of the type having at least two cone-pulley pairs.
In known transmissions of this type, one axially displaceable cone-pulley of each pair is formed as a rotating pressure cylinder of a piston firmly connected with the associated shaft, and the pressure application forces are generated hydraulically in the cylinder in dependence upon load and transmission ratio. Such transmissions are further provided with a transmission ratio setting member and a control slide valve coupled therewith which distributes the pressure fluid to the pressure cylinders, at least one adjustable pressure control valve controlling the application pressure, in dependence upon load and transmission ratio, in the return conduit of the control slide valve for the hydraulic pressure necessary on the drive-output side of the transmission. The pressure control valve, to which the pressure medium flows by way of a branch of an axially parallel bore in the associated shaft, is arranged on the drive-input and/or drive-output side of the transmission and is mechanically adjustable in dependence upon the torque transmitted on the corresponding transmission side and upon the axial position of the relevant displaceable cone-pulley. The pressure control valve body is actuatable by a movable intermediate member, e.g. a ball, which rests against a substantially axially parallel wedge face of a V-shaped groove of the associated axially displaceable cone-pulley, and the inclination of the wedge face varies over its axial length for the transmission ratio-dependent influencing of the pressure control valve.
Transmissions of this type are described in FRG Pat. No. 1,816,949 and corresponding U.S. Pat. No. 3,596,528. The pressure control valves described therein are radially displaceably arranged with their valve body in the associated shafts while the ball forming the intermediate member extends into a V-shaped groove which is arranged axially parallel with the shaft in the neck of the associated axially displaceable cone-pulley.
It has been found that this accommodation of the pressure control valve in the shaft together with the associated passages for the pressure fluid raises technological problems relating to manufacture and maintenance of the desired pressure levels. The thickness of the shaft limits the possibility of accommodating the radial sliding seat for the valve body there without the danger of weakening the bearing cross-section of the shaft. The same applies to the various pressure fluid conduits. Likewise it is complicated to manufacture the V-shaped groove for the valve ball in the interior of the hub of the axially displaceable cone-pulley. The valve body of the pressure control valve must here have the smallest possible diameter, so that the pressure oil forces acting at the end upon it must be relatively high in order to bring about the desired control function.
These difficulties could be counteracted by giving the respective shaft a correspondingly larger diameter. This, however, would entail an unnecessary expenditure for material and would increase the total mass to be moved.